Apparatus for heat-setting a tubular article of crystallizable polymer

Abstract

For making open-ended thermoplastic tubular articles, which are dimensionally stable up to elevated temperatures, an open-ended polymer tube is placed between a fixed, heated external mould and a cooled mandrel, which is vertically displaceable relative to the mould, both the ends of the polymer tube being clamped to restrain the tube axially. The polymer tube is radially expanded into contact with the hot mould and maintained in contact for a time sufficient to ensure dimensional stability, and then allowed to shrink back into contact with the cooled mandrel, which is maintained at a temperature below the glass transistion temperature of the polymer. The resulting article is then stripped from the mandrel.

I claim: 
     
       1. Apparatus for heat setting a preformed thermoplastic tubular article of a crystallisable polymer, which is open at both ends and which will be dimensionally stable up to a specific elevated temperature, comprising a mandrel, cooling means for cooling the mandrel to a temperature below the glass transition temperature of the tubular article, a mould having a cavity of complementary shape to that of the mandrel and surrounding the mandrel with a small clearance between the mandrel and mould, heating means for heating the mould to a temperature higher than said specific elevated temperature, clamping means for clamping each end of said article between the mandrel and mould for axially restraining said article and expansion means for elastically expanding the tubular article into contact with the mould. 
     
     
       2. Apparatus as claimed in claim 1, wherein the mandrel and mould are movable axially relative to one another. 
     
     
       3. Apparatus as claimed in claim 1 wherein the mandrel and mould are movable both axially and pivotally relative to one another to permit said preformed thermoplastic tubular article to be mounted on and removed from said mandrel. 
     
     
       4. Apparatus as claimed in claim 1, further comprising means for applying a vacuum to the mould cavity. 
     
     
       5. Apparatus as claimed in claim 4 wherein the expansion means comprises a means for applying a vacuum to the mould cavity. 
     
     
       6. Apparatus as claimed in claim 1, wherein the mandrel is hollow and has perforations in its surface, the expansion means comprising a conduit for supplying pressurised fluid to the interior of the mandrel. 
     
     
       7. Apparatus as claimed in claim 1, wherein the mould comprises a mould wall made of an air-permeable material. 
     
     
       8. Apparatus as claimed in claim 1, wherein the clamping means comprises, adjacent each end of the mandrel, an inflatable toroid of a resilient material, which cooperates when inflated, with respective surfaces on the mould to clamp said ends of the tubular article therebetween. 
     
     
       9. Apparatus as claimed in 1, wherein the clamping means comprises a pair of split-ring clamps, each having a fixed half-ring and a movable half-ring reciprocable relative to the fixed half-ring, wherein the ends of the tubular article can be squeezed between each clamp and the mandrel. 
     
     
       10. Apparatus as claimed in claim 1, wherein the mandrel is hollow and the cooling means comprises a helical conduit of a material of high thermal conductivity in thermal contact with the internal surface of the hollow mandrel, the conduit being served by cooling fluid supply and return means. 
     
     
       11. Apparatus as claimed in claim 1, wherein the heating means comprise band heaters wrapped around the external surface of the mould wall.